使Swift类符合需要init的协议 [英] Making a Swift class conform to a protocol that requires an init

问题描述

我在中有以下协议：Swift ：

I have the following protocol in Swift:

protocol FooConvertible{
    typealias FooType

    init(foo: FooType)
}

我可以使 Swift 类符合类定义：

I can make Swift classes conform to it in the class definition:

class Bar: FooConvertible {
    var baz: String = ""
    required init(foo: String){
        baz = foo
    }
}

但是，当我试图使一个类符合它在一个扩展（使用Cocoa类，它是我唯一的选择，因为我没有源），问题出现：

So far so good. However, the problem arises when I try to make a class conform to it in an extension (With Cocoa classes, it's my only option, as I don't have the source):

class Baz {
    var baz = ""
}

extension Baz: FooConvertible{

    required convenience init(foo: String) { // Insists that this should be in the class definition
        baz = foo
    }
}

extension NSURL: FooConvertible{

    required convenience init(foo: String) { // this also fails for the same reason

    }
}

这过去可能

这是因为它被删除的原因是什么？

What's the reason it was removed?

意味着所有XXXLiteralConvertible协议被禁止Cocoa类！

That would mean that all the XXXLiteralConvertible Protocols are banned from Cocoa classes!

推荐答案

您尝试创建此类内容的任何机会：

Any chance you are trying to create something like this:

protocol FooConvertible : class {
    typealias FooType

    var baz : String { get set } // protocol extensions inits may need to know this

    init(foo: FooType) // this is your designated initializer
}

extension FooConvertible {

    // init(foo: String) {
    //     self.init(foo: foo)
    //     baz = foo
    // }
    // you can't do this because it could call it self recursively 

    init(num: Int) { // this init will call your designated init and can instantiate correctly 
        self.init(foo: "\(num)")
    }
}

class Baz {
    var baz = ""
}

class Bar: FooConvertible {
    var baz: String = ""

    required init(foo: String) { // designated initializer
        baz = foo
    }
}

现在将了解 FooConvertible / code>。
如果是这样，我很高兴我可以帮助。 ：）

Baz will now know about all inits of FooConvertible. If so, I'm glad I could help. :)

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